Mixed Alkali-Ion Transport and Storage in Atomic-Disordered Honeycomb Layered $\rm NaKNi_2TeO_6$

TL;DR

This study introduces a novel mixed alkali honeycomb layered oxide, NaKNi2TeO6, demonstrating its unique atomic disorder and potential for dual-ion electrochemical storage with promising voltage and capacity.

Contribution

The paper reports the synthesis and characterization of NaKNi2TeO6, revealing atomic disorder and exploring its mixed Na/K ion transport and storage capabilities for energy applications.

Findings

Atomic structural disorder characterized by aperiodic stacking.

Achieved an average cell voltage of about 4 V.

Obtained a specific capacity of around 80 mAh g^{-1}.

Abstract

Honeycomb layered oxides constitute an emerging class of materials that show interesting physicochemical and electrochemical properties. However, the development of these materials is still limited. Here, we report the combined use of alkali atoms ($\rm Na$ and $\rm K$) to produce a mixed alkali honeycomb layered oxide material, namely, $\rm NaKNi_2TeO_6$. Via transmission electron microscopy measurements, we reveal the local atomic structural disorders characterised by aperiodic stacking and incoherency in the alternating arrangement of $\rm Na$ and $\rm K$ atoms. We also investigate the possibility of mixed electrochemical transport and storage of $\rm Na$ and $\rm K$ ions in $\rm NaKNi_2TeO_6$. In particular, we report an average discharge cell voltage of about $4\, \rm V$ and a specific capacity of around $80\, \rm mAh\, g^{-1}$ at low specific currents (i.e., $< 10\, \rm mA\, g^{-1}$) when a $\rm NaKNi_2TeO_6$-based positive electrode is combined with a room-temperature $\rm NaK$ liquid alloy negative electrode using an ionic liquid-based electrolyte solution. These results represent a step towards the use of tailored cathode active materials for dendrite-free electrochemical energy storage systems exploiting room-temperature liquid alkali metal alloy materials.